1. Field of the Invention
The present invention relates to a method and apparatus for determining the position of a catheter inside the body of a patient from position signals transmitted between the catheter and a remote position location unit.
2. Description of the Prior Art
For determining the position of e.g. the tip of a catheter inside the body (i.e. an endoceliac catheter), for example in a blood vessel or a cavity of the heart, or in the imaging of internal organs by mapping, the heterogeneity and, accordingly, the varying physical properties of adjacent tissues and even the presence of other objects in or outside the body can cause distortion, to a greater or lesser degree, in position determination or geometry depiction. This effect can be considerable in the use of ultrasound because of e.g. variation in the density of tissues and the velocity of sound. If electromagnetic methods are used, the variation in e.g. electrical conductivity, relative permittivity and relative permeability can affect measurement accuracy.
In non-medical applications, such as astronomy and remote sensing, corrections can be made for both constant and time-related aberrations in the atmosphere and measuring system by observing a reference object with a known shape in the ray path or close to the observed object.
In the brochure "A new method for non-fluoroscopic catheter based endocardial mapping", published by Ben-Haim et al., a technique is described for endocardial mapping with a non-fluoroscopic catheter in which a number of radiographs are first taken of a heart catheter located in a number of different positions in a ventricle of a heart.